Machine for sharpening screwing taps and the like



March 21, 1933. w. HUNT ET AL 1.902,.240

MACHINE FOR SHARPENING SCREWING TAPS AND THE LIKE Filed Aug. 5, 1951 s Sheets-Sheet 1 March 21; 1933 H, w. HUNT ET AL 1,902,240

MACHINE FOR SHARPENING SCREWING TAPS AND THE LIKE Filed Aug. 5, 1951 5 Sheets-Sheet 2 March 21, 1933. w T- r AL 1,902,240

MACHINE FOR SHARPENING SCREWING TAPS AND THE LIKE Filed Aug. 3, 1931 3 Sheets-Sheet Patented Mar. 21, 1933 iv I UNITED STATES PATENT HER ERT WILLIAM HUNT AND PERCY new, on manonns'rna. ENGLAND MACHINE For. sHAnmiN Ne SCREWING 'mrs AND 'IHELIKEO Application filed August 3, 1931-,--Serial- No. 554,766; and in Great Britain- August 19; 1930.

Thisinvention refers to a new or improvedconstruction of machine for sharpening or resharpemng screwing taps and the l1ke. I i

screwing taps are made'wlth a tapered or bevelled end, and such tapering. or bevelling is given a backing off. Resharpening of screwing taps is commonly effected by grinding back the teeth at the flutes. The prmcipal wear on a tap however, occurs at the leading orbevelled end, so that the taps can also. be sharpened by taking the bevelling further back which, while shortening the tap, does not thin or weaken the teeth.

The object of the invention is to enable the bevelling to be applied to taps efficiently and uniformly.

According to the invention, the improved tap sharpening or resharpening machine comprises means for holding and rotating the tap and means for simultaneously advancing and withdrawing the tap laterally with respect to a grinding wheel for each cutting edge.

In the accompanying drawin s:

.Figpl is .a front elevation o thequpper part of one example of tap grinding machine made in accordance with the invention.

Fig. 2- is a plan of Fig. 1.

3 Fig. 3 is an end elevation.

Fig; 4 is'a front elevation of the head stock and tailstock unit.

Fig. 5 .is anend elevation of Fig. 4. Fig. 6 is a sectional elevation-on line ,6-6 of Fig.4. p p Fig. 7 is a detail View of the stop plate.

As illustrated, the machine comprises a pedestal 10, the upper part only of which is shown, on which is mounted the usual tray 11 and the grinding .wheel 12. The spindle of the grinding wheel 12 is mounted in a bracket 13, and is provided with fast and loose pulleys. 14 and 15.- .Formed asypart of the tray are brackets 16 for a slide bar .4 17 and at the front edge of the tray a machined sliding face 18 below which is formed a groove 19. The main carriage 20 rests on the slide bar 17 and the sliding face 18 and is held to the bar 17 by half bearings secured by bolts 21 and. to the sliding faceby a retaini-ng piece 22fl'1aving. a projection engag ing. the groove 19 and securedto the slide by bolts-23. .The tray 11 has lugs 24 carrys ing a slidegscrew' 25having 31I1,-: 0])BIat1I1g: wheel 26. The main slideQO is formed with a depending lug 27 screwed to fit on the slide screw 25;. On the upper face oii-the main slide 20 is asupportinglug 28 and upstanding slide lugs 29 and 30 which latter are-undercut to receive a slide 31. The front lug '29 is screwed for a slide screw 32pmvided with an operating wheel 33, the screw being joined ina-lug 34 atthefront end of the slide. Projecting from one side of-the. slide is a web 35 on the upper face of which 6 is formed a. quadrant 36 which will be graduated in degrees of angularity. The under side of the web" is formed with a machined face to engage with the face of the supporting lug 28. On: the other side of the slide 79 31 is a lug 37 for a vertical pivot which forms the centre of the quadrant. Supported on the upper face of the. quadrant 36 and lug :37 is an undercut slide rail 38 secured by bolts having; clamping nuts 39 and 40, the nut 39 holding a retaining plate 41. On the slide rail 38 are brackets 42 and 43' which carry an overhan 'ging shaft 44 on which are keyed the handstock45 andtailstock 46. The brackets 42 and 4-3 are adjustably secured on the slide rail 38'by wing nuts 42 and 43; On the bracket .42: is

formed an upstanding lug 47 onthe side of which is mountedv an abutment roller48 and in whichlug 47 is housed aspring49 for 5 i the tiebolt 50 connected to theheadstock.

In the headstock is mounted the chuck spindle, onone end of which is mounted Y the'chuck51. In the bearing oftheheadstock is a friction pad 52 engaging the chuck spindle and having a springy53land adjustable nut "54 toregulate; the pressure. On. the chuck 'spindlebehind the headstock bearing is a leverv handle 55, rotatable on. the spindle. On the side of the leyer "handle against. the headstock bearing is sup,- ported a cam plate 56 located-ona stu'd 57 and .an eccentric 58. in; the face of the leyer, (see Fig. 6):. {Theeccentric 58 is provided with pointer v59 co-operating with a scale 1 and 65, marked A and B respectively to en-,.. gage the ratchet wheels. On the end of the I chuck spindleisa stop plate 66 having a stop lug 67 projecting'acrossthe front of. the ratchet wheels to be engaged by the pawls 64 or 65., The stop plate is graduatedand held in any desired position by a clamp 68 fastened/byja clamping nut '69 .to the end of the shaft 44. The lever 55 has a'stop 7Q engaging a:projection 71 on the foot 72 of-the headstock by which the headstock is mounted onthe shaft 44;

For grinding the flutes ofthe taps an attachment is provided in a bracket 73 secured-to the back of the grinding wheel bracket 13, vand consisting of an arm 74 carryinga grinding wheel 75 and embodyingsuitable shafts and bevel wheel drive, fast and loose driving pulleys 76 and 77 being" provided. The arm 74 can be brought down to engage the tap, being pivoted about the driving shaft in the bracket 73and is provided with an adjustable stop screw 78 adapted to position the heightof the wheel overthe tap by en gaging a lug 79. p 7

Instead of belt drive, electric motors may be'coupled direct to the grinding wheels.

In operation, the machineis operated by the simple action of giving the lever arm a to-a-nd-fro 1novement between its stops. The stop plate 66 is set according to the number of flutes on the-tapso that the movement of the lever arm gives the tap a part rotation being A; of a turn for a three flute tap, and so on. The plate is graduated with the number and letters 1 as follows BAAA -BABAA, '8456- 789-1012--- The letters A and B indicate the pawl to be used for the setting chosen and as will be seen bring into use the ratchet wheel having the number of teeth which is a multiple of the number of flutes. I

The tap is presented to the grinding wheel by'means-of the operating wheels 33 and 26 and is set in the chuck in the first instance by a verticalstraight-edge placed across a flute, which setting allows the grinding of each set of teeth to be car'- ried to the "extreme back edge without catching the front or cutting edge-of the next set of-teeth against the grindingwheel. The setting of'the cam forthe-backing off is obtained by means of theeccentric, the positionjof whichis indicated by the pointer 59 the rotation of the eccentric causing the cam plate 56 to be raised or lowered, the lateral movement being substantially negligible and of no effect.

The headstock and tailstock rock on the shaft 44 with each movement of the operating lever 55 by reason of the cam 56 engaging the abutment roller 48, the spring 49 holding the headstock cam against the roller. The tap is thus given an advancing or withdrawal movement simultaneously with each part rotation as'the handle is pulled down and is. again withdrawn or advanced without'rotation as the operating lever is returned, the friction pad 52 holding the chuck spindle from rotation. v

- The above combined movement gives the required backing oif and equallyto. each set-of teeth.

The taper to be given to the tap is determined by the angular setting as indicated at the quadrant 36.: 1.

For grinding the flutes, the angular setting is returned to zeroand the wheel 33 operated-to bring the tap away from the grinding wheel 12' and into position for the wheel 75. All the flutes maybe ground to the same depth and the cuttingedges'to the correct part'rotation of the tap. 1

In the matter of constructional details, variations may be made in the machine without departing from the-invention, the essential features of which are (1) themovement ofthe tap rotationally and bodily while in contact withthe grinding wheel, and (2) the provision of means -for varying the rotational movements to suitthe make of tap to'be' sharpened. I I a 1. In a grinding machine forsharpening screwing taps and the like having a head stock and tailstock mounted to rock about an axis parallel to the axis of the tap and having a cam on the headstock engaging a fixed abutment to produce such rockingmotion synchronously with the rotation of the headstock, in combination, a lever rotatably mounted on the axis of theheadstock, and carrying the cam, a ratchet wheel secured on the spindle'of the-headstock adjacent to the lever, a pawl on the lever to engage the ratchet wheel, means forpr'eventing thereverse rotation of the headstock and adjustable means for limiting thearc of movement of thelever; I

2; In a grinding machine for sharpening screwing taps according to claim 1, two ratchet wheels adjacent to the lever havim a diflerent number'of teeth, a pawl'for eac wheel onthe lever and'means for holding either p awl"out of engagement with its wheel.

In agrinding machinefor sharpening screwlng'taps as' claim'ed in claim '1 the means for limiting the arc of movement of the leverconsisting of a calibrated quadrantshaped plate on the axis of the headstock with a stop project-ion lying in the path of the pawl, and a clamp on the base of the headstock to hold the plate in a set position.

4. In a grinding machine for-sharpening screwing taps and the like according to claim 1, a main grinding Wheel supported in fixed bearings, an auxiliary flute-grinding wheel rotating at right angles to the main grinding wheel and supported in pivotally mounted bearings so as to be moved into and out of grinding position, guides-parallel with the axis of the main grinding wheel, a slide mounted on the guides and a headstock carrier pivotally mounted on the slide so as to be adjustable to bring the tap into the plane of each wheel and at a different angle to each plane.

In testimony whereof We have signed our names to this specification.

HERBERT WILLIAM HUNT. PERCY HUNT. v i 

